1. Field of the Invention
This invention relates generally to an electronic component wherein the electronic component contains pads and the components are joined together by solder and/or socket interconnections with other components and, more particularly, to the rework of such electronic component containing copper or copper/nickel pads having a layer of nickel and an overlying layer of gold by removing the gold and nickel layers on the pads and returning the pads to their original condition as on prime parts.
2. Description of Related Art
Forming an electronic package assembly whereby an electrical component such as an integrated circuit chip is electrically and mechanically connected to a substrate, a card, or board, another chip or another electronic part is well-known in the art. This technology is generally termed surface mount technology (SMT) and has gained acceptance as the preferred means of making electronic package assemblies. The interconnect technology is known as ball grid array packaging, C4 flip chip interconnect, multi-chip modules, multilayer and micro via printed wiring boards and surface mount hybrid assembly. In one particular application, to which this application is directed to for convenience, a multilayer glass-ceramic component is joined to a chip and/or an organic substrate. Such glass-ceramic component is to be reworked by removing defective metallization layers from the pads and returning them to their original condition.
Multilayer glass-ceramic electronic components are typically joined to other components by soldering pads on a surface of one of the electronic components to corresponding soldering pads on the surface of the other component. Control Collapse Chip Connection is an interconnect technology developed by IBM as an alternative to wirebonding. This technology is generally known as C4 technology or flip chip packaging. Broadly stated, an integrated circuit chip is mounted above a glass-ceramic substrate and pads on the chip are electrically and mechanically connected to corresponding pads on the substrate by a plurality of electrical connections such as solder bumps to form a module. A module is typically connected to other electronic components by solder or socket type connections.
In the C4 interconnect technology, a relatively small solder bump is attached to the pads on one of the components being joined, typically to the chip. The electrical and mechanical interconnects are then formed by positioning the corresponding pads on the glass-ceramic substrate to be joined adjacent the solder bumps on the chip and reflowing the bumps at an elevated temperature. The C4 joining process is self-aligning in that the wetting action of the solder will align the chip bump pattern to the corresponding pads on the glass-ceramic substrate.
A myriad of solder structures have been proposed for the surface mounting of one electronic component to another. Typical surface mount processes form the solder structures by screening solder paste on conductive, generally metallic pads exposed on the surface of a card or substrate. The solder paste is reflowed in an inert atmosphere and homogenizes the pad and brings the solder into a spherical shape. After alignment of corresponding pads the whole assembly goes through a reflow operation to form solder bonds. The interconnection made by joining components by an array of solder balls is termed a ball grid array (BGA). When the solder structure is in the form of a column, it is termed a column grid array (CGA). Land grid array (LGA) interconnection is used in socket type electronic assemblies.
Glass-ceramic substrates typically contain copper or copper/nickel pads which have a finishing metallurgy of a nickel layer on the copper pad followed by a gold layer which finishing metallurgy is required to produce solder wettable and socketable surfaces. Electroless plating of a nickel/phosphorous (NiP) layer followed by plating of a gold layer is typically used to make the finishing metallurgy. Since the plated layers may be defective it is necessary that the rework process restores the pads to their initial condition before the substrate can be replated and joined to another component.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for reworking electronic components having copper or copper/nickel pads with nickel and gold layers to restore the pads to their original condition.
It is another object of the present invention to provide an apparatus for reworking electronic components having copper or copper/nickel pads with nickel and gold layers to restore the pads to their original condition.
It is yet another object of the present invention to provide an electronic component substrate and/or assembly reworked using the method and apparatus of the invention.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.